docs: def add_highlight(self, field, fragment_size=None,
                        number_of_fragments=None, fragment_offset=None, type=None):
          """Add a highlight field.
  
          The Search object will be returned, so calls to this can be chained.
  
          """
          if self._highlight is None:
              self._highlight = HighLighter("<b>", "</b>")
          self._highlight.add_field(field, fragment_size, number_of_fragments, fragment_offset, type=type)
          return self